Internal Combustion-Electric Hybrids

By Carey Russ (c) 2003



One automotive ``technology of the future'' is an accepted 

technology of the present. Gasoline-electric hybrid vehicles, if not 

commonplace, are readily available from several manufacturers. 

They combine an internal-combustion engine with batteries and an 

electric motor to produce motive power. Depending on the system 

design, hybrid vehicles can operate on internal combustion or 

purely electric power, or a combination of each. The electric motor 

may do double duty as the internal combustion engine's starter 

motor. During deceleration, it also functions as a generator, to 

recharge the storage batteries. As an added benefit, magnetic drag 

produced in generator mode contributes to the braking efficiency 

of the vehicle. 



Broadly speaking, there are two ways to categorize hybrid systems. 

Series designs use the internal combustion engine to charge 

batteries, which provide power to the electric motor or motors that 

turn the wheels. In parallel systems, the internal combustion engine 

is used to both provide tractive power and charge the batteries, and 

the electric motor also provides tractive power. Depending on 

conditions, the vehicle may operate under purely internal 

combustion power, purely electric power, or a combination of 

both. 



Toyota was the first to market with the first-generation Prius in 

Japan in the late 1990s. Although Toyota brought a few early 

Priuses to the U.S. for evaluation, Honda beat them to market here 

when it introduced the Insight in late 1999. The American-spec 

Prius debuted a few months later. For the 2003 model year, they 

were joined by the Honda Civic Hybrid. Toyota debuted the 

second American-generation Prius recently, and has announced 

that a hybrid model of the popular Lexus RX330 SUV will be 

available in the future. Ford has announced that a hybrid version of 

its Escape SUV will be offered in about a year, with a hybrid 

model of its upcoming Futura mid-sized sedan planned. General 

Motors has a number of hybrids in development, including full-

sized pickups, SUVs and sedans of all sizes, and even a diesel-

electric bus. Other manufacturers are working on hybrids as well.



All current automotive hybrid systems are parallel in nature, 

although they vary in complexity. Honda's ``Integrated Motor 

Assist'' (IMA) is among the simplest. The electric motor assists the 

gasoline engine when extra power is needed; an Insight or Civic 

Hybrid never operates as a purely electric vehicle. Despite its 

simplicity, IMA does significantly improve efficiency, primarily 

because a smaller, more-efficient gasoline engine can be used than 

if there was no IMA. The Prius and other announced hybrids are 

considerably more complex. Although they normally operate under 

a combination of gasoline and electric power, they can run (rarely) 

as purely gasoline or (more commonly) purely electric vehicles.



It is also possible to drive one set of wheels with an internal-

combustion engine and the other with electric power in a hybrid 

four-wheel drive system. There is also absolutely no reason that 

the gasoline engine in a hybrid cannot be replaced by a diesel for 

even greater efficiency. The next ten years are going to be very 

interesting in terms of hybrid technology. 



A little off-topic, but.... Hybrid systems are not found only on 

roads. In the 1930s, to reduce air pollution caused by steam 

locomotives in urban environments, General Electric developed 

diesel-electric switching locomotives in which the diesel engine 

was used to run a generator to charge storage batteries that drove 

the traction motors. At 300 horsepower, they were strong enough 

for the light-duty requirements of their day, but quickly became 

obsolete. 



All railroad-sized diesel locomotives in use in North America 

today are diesel-electric designs, but they differ significantly from 

automotive hybrids in that no storage batteries are used. Electric, 

rather than mechanical or hydraulic (torque converter) power 

transmission is used because electric traction motors can stand up 

to the power necessary to move a heavy train. And, as with 

regenerative braking in hybrid cars, the traction motors can be used 

to help slow a train, although the energy generated is converted to 

heat and dissipated through heavy-duty resistors. Mechanical and 

hydraulic transmission systems have been used successfully in 

small industrial switching locomotives with a few hundred 

horsepower, but were abject failures in main-line service in 

locomotives with 4,000 horsepower and many, many lb-ft of 

torque.